The High Voltage Electron Microscope Facility is a Biotechnology Resource of the Biotechnology Resources Branch and is available to biomedical researchers for ultrastructral studies where use of a high voltage electron microscope can provide new information. The application will be directed specially towards analysis of relatively large and complex three-dimensional cell structures either in intact cells or isolated organelles or in sections up to 1 or 2 micron m thick. The possibility for imaging undehydrated biological specimens in special environmental chambers (specimen holders) will be investigated. Methods of image analysis applicable to thick biological specimens will be developed.